1. Combine dashi stock, soy sauce, mirin, and sugar in sauce pan over medium heat bring to boil.
2. Add chicken and simmer on low heat until partially cooked. Add onion slices and simmer until chicken is just cooked.
3. Lightly beat eggs in a bowl, bring soup to boil, and pour eggs over chicken and onion. Turn heat down to very low, and cover with lid for about one minute, turn off heat.
6. Serve on hot cooked rice in individual serving bowls. Garnish with spring onions and sengiri shoga.